The present invention relates generally to a wood boring drill bit and more particularly to a wood boring drill bit having an easily retractable cutting head with helical-shaped cutting wings and a self-feeding pilot screw.
Flat one piece wood boring drill bits, commonly known as spade drill bits, are widely used for boring holes in wood. However, spade drill bits are generally thin and effective only for occasional or light duty drilling. A heavier and more substantial cutting head is needed and desirable for drilling large diameter holes. Also a heavier cutting head is needed for drilling a large number of holes or for drilling holes through thick material or hard wood or composite materials.
Contractors and professional builders prefer heavy duty wood-boring bits with a helical-shaped cutting head and a self-feeding pilot screw. A sturdy helical cutting head performs better than a flat spade bit because the helical cutting head cuts faster and requires little axial force. Also, these heavier drill bits generally have a pilot screw with tapered threads to pull the cutting head into the wood. However, these heavier cutting heads have certain disadvantages.
One disadvantage of presently known helical cutting heads is that the cutting heads have a square profile. The squared trailing surfaces of the cutting head often hang up or snag on the exit end of the drilled hole when the cutting head is being retracted through the hole.
Another disadvantage of known cutting heads is that the pilot screw can be dulled or damaged through use or when the drill bit encounters hard material. It is often difficult to sharpen or repair the pilot screw. If the pilot screw is permanently attached to the cutting head and shank, the whole drill bit may have to be replaced. If the pilot screw is permanently attached to only the cutting head, the cutting head and pilot screw may have to be replaced. If the pilot screw is a permanent part of the shank, the pilot screw and shank portion may have to be replaced.
Another disadvantage of known cutting heads is that the cutting heads are permanently attached to a fixed length shank. A cutting head that is permanently attached to a shank does not allow the drill user any flexibility in configuring the drill bit assembly for the specific drilling situation. Therefore, the present invention provides a self-feeding, wood boring drill bit which overcomes many of the problems of known cutting heads.
The present invention provides a smoothly tapering trailing surface on the cutting head that tapers from the side surfaces of the wings to a point near the shank. The tapered trailing surface allows smooth retraction of the cutting head from a drilled hole.
The present invention also provides a replaceable pilot screw as part of the cutting head. The cutting head has an axial bore for receiving a replaceable pilot screw and a set screw for locking the pilot screw in place.
The present invention also provides a short stem on the rear of the cutting head for receiving a separate shank. The stem allows the user to configure the drill bit for the specific situation.